Improvements relating to lawnmowers and in particular robotic lawnmowers

ABSTRACT

Aspects of a lawnmower and in particular a robotic lawnmower are disclosed herein. Specifically, the lawnmower may include a passive cleaning assembly for removing detritus from the housing, the passive cleaning assembly being moveably mounted on said housing. Movement of the lawnmower with respect to the ground may cause a cleaning portion of the passive cleaning assembly to move with respect to the housing and thereby remove detritus from the housing. In one aspect, the lawnmower may be configured such that, during use, the cleaning assembly is moved with respect to the housing thereby causing a scraping edge of a cleaning portion of the cleaning assembly to move with respect to the housing and thereby scrape detritus off the housing. In another aspect the lawnmower may comprise a sliding member having a ground-engaging surface that is positioned so as to face towards and to slide over the ground during such movement of the lawnmower over the lawn. In another aspect the lawnmower may comprise a ground contact footprint being defined by a polygon bounding a plurality of ground contact regions. In addition, at least part of one or more of the cutting areas swept out by the grass cutting blades may be positioned beyond the perimeter of the ground contact footprint, at the front of the lawnmower with respect to its forwards direction of movement.

TECHNICAL FIELD

The present invention relates to home robotics in general and to roboticlawnmowers in particular; it also relates, in some aspects, tolawnmowers generally, as well as robotic lawnmowers.

BACKGROUND

The use of automated devices is widespread nowadays, and finds countlessapplications. By their very nature, autonomous machines such as robotsrepresent a significant labour-saving for consumers. Repetitive andtime-consuming tasks may now be carried out without significantsupervision or instruction by the user of such autonomous machines.

Robotic lawnmowers are a particularly commercially successful example ofsuch an autonomous moving machine, substantially reducing the time andeffort required on the user's part in order to maintain a neatly-keptlawn.

A number of robotic lawnmowers are currently available to the consumer,such as the RC and RS series from Robomow™. However, in many respects,robotic lawnmowers have not yet been perfected and improvements maystill be achieved, for example in terms of reliability, ease of useand/or efficiency.

SUMMARY

Aspects of the invention are set out in the appended claims.

The following disclosure, in one aspect, describes a lawnmower thatcomprises: a housing; and a passive cleaning assembly for removingdetritus from the housing, the passive cleaning assembly being moveablymounted on said housing. Movement of the lawnmower with respect to theground causes a cleaning portion of the passive cleaning assembly tomove with respect to the housing and thereby remove detritus from thehousing

In a further aspect, the following disclosure describes a lawnmowercomprising: a housing; and a cleaning assembly for removing detritusfrom the housing, the cleaning assembly being moveably mounted on saidhousing. The lawnmower is configured such that, during use, the cleaningassembly is moved with respect to the housing thereby causing a scrapingedge of a cleaning portion of the cleaning assembly to move with respectto the housing and thereby scrape detritus off the housing.

In a still further aspect, the following disclosure describes a roboticlawnmower comprising: two driven wheels for moving the lawnmower overthe lawn; and a sliding member having a ground-engaging surface that ispositioned so as to face towards and to slide over the ground duringsuch movement of the lawnmower over the lawn. The sliding member and thetwo driven wheels are positioned at opposing ends of the lawnmower suchthat the sliding member and the two driven wheels support respectiveportions of the lawnmower's weight.

In yet a further aspect, the following disclosure describes a roboticlawnmower comprising: a housing; a plurality of ground-contactingmembers, which during use each contact the ground over a ground contactregion, the ground-contacting members thereby supporting the housingabove the ground, at least some of said ground-contacting members beingdriven so as to move relative to the housing and to the ground therebypropelling the lawnmower over the ground, a ground contact footprintbeing defined by the polygon bounding all of said ground contactregions. The lawnmower further comprises at least one grass cuttingblade, each of which is driven by the lawnmower so as to move withrespect to the housing, thereby sweeping out a respective cutting areabeneath the housing. At least part of one or more of the cutting areasis beyond the perimeter of said ground contact footprint.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now directed to the drawings, in which:

FIG. 1 illustrates schematically an example of a robotic lawnmower andthe systems thereof;

FIG. 2 is a perspective view of the back of a robotic lawnmower in whichvarious concepts disclosed herein are embodied;

FIG. 3 is a perspective view of the front of the robot of FIG. 2;

FIG. 4 is a perspective view of the robot of FIG. 2 approaching acharging station;

FIG. 5 is a perspective view of the robot of FIG. 2 docked at thecharging station shown in FIG. 4;

FIG. 6 is a perspective view of the underside of the robot of FIGS. 2 to5, which illustrates the relative disposition of a housing, a cleaningassembly, a sliding member, a cutting blade, and two driven wheels ofthe robot;

FIG. 7 is a detail view of the relative disposition of the housing, thecleaning assembly, and the cutting blade illustrated in FIG. 6;

FIG. 8 is a detail view of the cleaning assembly illustrated in FIG. 6;

FIG. 9 is a detail view of the housing illustrated in FIG. 6;

FIG. 10a is a perspective view of the cleaning assembly in a firstposition with respect to the housing of the robot of FIGS. 2 to 7;

FIG. 10b is a perspective view of the cleaning assembly in a secondposition with respect to the housing of the robot of FIGS. 2 to 7;

FIG. 11 is a plan view of the underside of the robot of FIGS. 2 to 7,illustrating the arrangement of the robot's cutting blade with respectto its wheels and sliding member; and

FIG. 12 is a schematic view of the robot of FIGS. 2 to 7 when movingaround a working area according to a movement pattern described herein.

DETAILED DESCRIPTION OF THE DRAWINGS

Overview

Turning first to FIG. 1, there is shown schematically an example of arobotic lawnmower 1, in which various concepts disclosed herein may beemployed, and details the systems included in such a robotic lawnmower.As is shown in the drawing, the robot 1 includes: a movement system 400,for moving the robot over the surface of the ground; a navigation system300, to enable the robot to navigate around a working area, such as aportion of, or the whole of, a lawn; a mowing system for mowing the lawn(or portions thereof); a power system 200, for powering the varioussystems, components etc. within the robot 1; a control system 100, forcommunicating with and controlling the systems of the robot 1; and auser interface 600, enabling the user to input commands, information andthe like to control the robot's operation and providing an indication tothe user of the robot's current state.

The control system 100 may, for example, include a main board, and allelectronics, as hardware, software and combinations thereof and othercomponents, necessary for the robot 1 to perform all of its operationsand functions (known as the main board electronics). The main board mayinclude one or more processors as part of the main board electronics.

As indicated in the drawing with solid lines, the navigation, movement,power, mowing and user interface systems are in data communication withthe control system, so that the control system can receive data fromand/or send instructions to these systems.

As shown by dotted lines in FIG. 1, the power system 200 is electricallyconnected to the control 100, navigation 300, movement 400 and mowing500 systems, and the user interface 600, so as to supply electricalpower to these systems and their components.

The power system 200 may, for example, include: an internal power source(typically rechargeable), including for instance one or more batteries;battery voltage sensors, typically for each battery, that enable therobot to determine when the power source is running low; and chargingcontacts, that enable connection to an external power source (which may,for example, be provided at a docking station) so as to allow theinternal power source to be charged.

The robot 1 may be designed such that it can be received by a dockingstation (not shown) which the robot 1 will return to once its task iscomplete (e.g. for orderly control and arrangement of the robot), and/orwhen its internal power source is running low. While in this dockingstation, various functions can occur, such as battery recharging,communication of operating data and the like.

The navigation system 300 may include a number of sensors that enablethe robot to navigate around the working area of the ground, when movingusing the movement system 400. Such sensors may, for example, include:

-   -   sensors operable to determine the robot's position relative to        the boundary of the area within which it is operating (for        example: coils for sensing a magnetic field induced by a wire        loop delimiting the area that transmits an alternating current;        range finders, such as ultrasonic or laser range finders, which        can measure a distance from a hard delimiter such as a fence or        wall; 2D or 3D machine vision systems that can evaluate a        distance to marked or natural delimiters);    -   sensors operable to sense the relative motion of the robot (e.g.        odometers, accelerometers, gyroscopes, magnetometers and the        like, for example provided in an inertial measurement unit); and    -   sensors operable to determine the robot's absolute position        within the area (e.g. satellite navigation system receivers,        local positioning system receivers, cameras or other sensor        arrays).

It should be noted that sensors may fall into several of thesecategories.

The movement system 400 may include driven wheels, continuous tracks andthe like, which are driven by one or more motors provided within thelawnmower, so as to move the lawnmower over the lawn.

The mowing system 500 may include one or more mowing blades driven byone or more motors so that the robot can cut the grass.

Turning now to the user interface 600, as noted above, this may enablethe user to input commands, information and the like to control therobot's operation and may provide an indication to the user of therobot's current state. Accordingly, it may include a number of controls,such as buttons, dials and the like, and a number of indicators, such asa display screen, LEDs and the like, or a combination of both, such as atouchscreen. It may also include a wireless communication link, so as toconnect with a user device, such as a smart-phone, tablet device,laptop, PC etc.

Attention is now directed to FIGS. 2 to 11, which illustrate a morespecific example of a robotic lawnmower 1, in which various conceptsdisclosed herein are embodied. The robotic lawnmower includes control100, power 200, navigation 300, movement 400, and mowing 500 systems anda user interface 600, which generally interact in the manner describedabove with reference to FIG. 1.

FIGS. 2 and 3 show, respectively, views of the back and front of therobotic lawnmower 1. As may be seen from these figures, the lawnmower 1includes a housing 2 that is supported above the ground by wheels 5linked to respective drive motors (not shown) within the housing 2. Thehousing 2 supports and/or contains many of the components of thelawnmower 1. The wheels 5 and drive motors form at least part of themovement system 400 for the robotic lawnmower 1.

As may be also seen from FIGS. 2 and 3, the lawnmower 1 includes acarrying handle 3 provided on the housing 2, with which the lawnmower 1can be lifted off the ground, and a play/pause button 6 with which theuser may interact with the robot and which thus forms a part of the userinterface 600 for the lawnmower 1. For example, when the user pressesthe play/pause button 6, the robot may switch between a paused state,where it remains stationary, and an active state, where it operatesaccording to a previously-selected one of a number of active modes (e.g.a return to charging station mode, a working mode, where it mows thelawn etc.).

As is shown in FIG. 2, the lawnmower further includes a slot 7 at itsrear end (with respect to its forwards direction of movement, indicatedby arrow F). At each end of this slot 7 there is provided acorresponding hole that is configured to receive a charging pin 51; arespective charging contact is located within each hole to electricallyconnect the power system 200 of the robot 1 with the charging pins 51.Such charging pins 61 may, for example, be provided on a chargingstation 50, so that when the robot 1 docks at the charging station 60 itmay recharge its internal power supply. FIGS. 4 and 5 illustrate,respectively, the robot 1 approaching a charging station 60 and therobot 1 docked at the charging station 50. As is apparent from acomparison of FIGS. 4 and 5, as the robot docks at the charging stationthe charging pins 61 are inserted into the holes provided within slot 7.An electrical connection is thereby made between the charging station 60and the robot 1, with the robot thereby being able to recharge itsinternal power supply.

It will of course be understood that the user interface 600 may includefurther additional elements, as discussed above with reference to FIG.1; moreover, in some cases, the user interface 600 may not include sucha play/pause button 6.

FIG. 6 shows a perspective view of the underside of the roboticlawnmower 1 of FIGS. 2 and 3. As can be seen from this figure, thelawnmower 1 includes wheels 5 a and 5 b disposed on two opposing sidesof the housing 2. More particularly, the wheels 5 a and 5 b are spacedapart along a wheel axis 33 and may be driven independently byrespective drive motors (not shown) so that they rotate about the wheelaxis 33 thereby propelling the lawnmower 1 along the ground. As thewheels are driven independently, the control system 100 of the robot isable to cause them to revolve at different rates, in order for the robotto carry out turning movements. The control system 100 is also able tocause the wheels 5 a, 5 b to revolve at the same rate, in order for therobot to move forwards (or backwards) along a straight line.

While the movement system 400 for the robot 1 is therefore capable ofdriving the robot in both a forwards direction (indicated by arrow F)and a backwards direction (as well as being capable of carrying outturning movements), it should be understood that the robot (for example,the control system 100 thereof) may be programmed such that the robotpreferentially drives in the forwards direction.

As may also be seen from FIG. 6, the housing 2 further includes aground-facing portion 9. In the particular example shown, theground-facing portion 9 is configured as a mowing deck and thereforesupports grass cutting blade 12 and its associated motor (not shown).During use, the grass cutting blade 12 is rotated at high speed by themotor, so as to cut an area of the lawn beneath the lawnmower 1. Thegrass cutting blade 12 and associated motor therefore form at least partof the mowing system 500 for the lawnmower 1.

Such a mowing deck 9 may be moveably suspended from the main part of thehousing. More particularly, it may be moveably suspended such that itmoves with respect to the housing depending on the height of the grass,the grass cutting blades being coupled to the mowing deck so as to movetherewith with respect to the housing. The mowing deck 9 may accordinglyinclude ground contacting portion that, during use of the lawnmower,rests on the ground, In the specific construction shown in FIGS. 6 and7, this ground contacting portion is a smooth lip at the outside edge ofthe mowing deck 9. The ground contacting portion may, in some cases, actto set the position (e.g. the height) of the mowing deck with respect tothe main part of the housing.

In the specific construction shown in FIGS. 6 and 7, the ground-facingportion/mowing deck 9 is coupled to the remainder of the housing 2 via aparallelogram linkage so that it can move up or down whilst remainingparallel to the ground plane, and can also be balanced by springs, inorder to minimize its ground pressure. An example of such aparallelogram linkage mechanism is described in WO 99/45757. Theparallelogram linkage may reduce the drag of the mowing deck 18 on thelawn, thus reducing its influence on the lawnmower's maneuverability.However, it will be appreciated that other arrangements for mounting themowing deck 18 may be used. For example, the mowing deck might besuspended from the remainder of the housing 2 using springs, or might besimply attached to the remainder of the housing 2.

Passive Cleaning Assembly

During use of a robotic lawnmower—and indeed lawnmowers moregenerally—detritus such as mulch, dirt and the like tends to accumulateon the housing of the robotic lawnmower. This may lead to reducedefficiency for the robot, since such detritus may cause increasedresistance to movement of the blade and/or the robot itself. Moreover,should large lumps of accumulated detritus suddenly detach, there is arisk that the robot becomes stuck on these; thus the accumulation ofdetritus may impact upon the reliability of the robot.

It is therefore envisaged to provide a robotic lawnmower that comprisesa housing and a passive cleaning assembly for removing detritus from thehousing. In some embodiments the housing may be generally bowl shaped.In some embodiments it also envisaged that the cleaning assembly may begenerally bowl shaped.

The passive cleaning assembly is moveably mounted on the housing. Moreparticularly, movement of the lawnmower with respect to the groundcauses a cleaning portion of the passive cleaning assembly to move withrespect to the housing and thereby remove detritus from the housing.

The robotic lawnmower shown in FIG. 6 includes an example of such apassive cleaning assembly 19. Reference is directed to FIGS. 7 to 9,which show in further detail this example of a cleaning assembly 19 andin which: FIG. 7 is a detail view of the arrangement of the housing 2,the cleaning assembly 19, and the cutting blade 12 illustrated in FIG.6; FIG. 8 is a detail view of the cleaning assembly 19 illustrated inFIG. 7; and FIG. 9 is a detail view of a ground-facing portion 9 of thehousing 2 of the robot.

The particular example of a cleaning assembly 19 shown in FIGS. 6 to 9includes, in addition to a cleaning portion 10 (which, as noted abovemoves with respect to the housing 2, thereby removing detritus from thehousing), a ground-contacting portion 11, which contacts the groundduring use, thereby causing the cleaning portion 10 to move with respectto the housing 2 during movement of the lawnmower. Thisground-contacting portion 11 may be adapted to contact the ground at therear of the lawnmower 1 with respect to its forward direction ofmovement (indicated by arrow F in the drawings).

In more detail, the particular example of a cleaning assembly 19 shownin FIGS. 6 to 9 is rotatably mounted on the housing 2. The cleaningassembly is thus able to rotate about a cleaning assembly axis 31, shownclearly in FIGS. 7 to 9. As is apparent, the axis about which the grasscutting blade 12 rotates is substantially aligned with this cleaningassembly axis 31. This may provide a particularly compact arrangement,as there is little risk of interference between the movement of thegrass cutting blade 12 and movement of the cleaning portion 10. As isalso apparent from FIGS. 7 to 9, the cleaning assembly axis 31 issubstantially normal to the ground.

With the particular example of a cleaning assembly 19 shown in FIGS. 6to 9, as the robotic lawnmower 1 moves around the lawn, only certainmovements of the lawnmower 1 with respect to the ground cause thecleaning portion 10 of the passive cleaning assembly 19 to rotate withrespect to the housing 2 (thereby removing detritus from the housing 2).Specifically, only turning movements of the lawnmower 1 cause thecleaning portion 10 to move with respect to the housing 2. By contrast,when the lawnmower 1 moves along a straight line (forwards or backwards)the cleaning portion 10 of the passive cleaning assembly 19 does notmove with respect to the housing 2.

The ground-contacting portion 11 may be configured such that the amountof friction between itself and the ground is substantially greater whenthe robot 1 carries out turning movements, as compared with when therobot 1 carries out straight-line movements. Accordingly, in theparticular example shown in FIGS. 6 to 9, the ground-contacting portion11 includes a number of chains 22 a, 22 b, 22 c which contact the groundduring movement of the robot 1. As the ground-contacting portion 11shown in FIGS. 6 to 9 is adapted to contact the ground at the rear ofthe lawnmower 1 with respect to its forward direction of movement(indicated by arrow F in the drawings) it might be compared with a“tail” for the robot 1.

Each of the chains is articulated such that it can only bend only in avertically oriented plane. In the specific example shown in FIGS. 6 to9, where the cleaning assembly 19 is rotatably mounted on the housing 2about cleaning assembly axis 31, each chain is articulated such that itcan bend only in a plane defined by the (vertical) cleaning assemblyaxis 31 and by a direction that extends generally radially with respectto the cleaning assembly axis 31.

In any case, when the robot moves over the ground in a straight line inthe forwards direction, the articulated chains 22 a, 22 b, 22 c aredragged over the lawn, flexing so as to accommodate the movement. Thus,a small amount of friction between the chains 22 a, 22 b, 22 c and theground may be expected. By contrast, when the robot 1 carries out aturning movement, the chains 22 a, 22 b, 22 c are unable to bend or flexto accommodate this movement and thus provide substantially greaterresistance to movement or friction. This, in turn, leads to the movementof the cleaning assembly 19 with respect to the housing 2 and therebythe cleaning of detritus from the housing 2 using cleaning portion 10.

FIG. 8 illustrates further details of the configuration of eacharticulated chain 22. As may be seen from the drawing, each chain 22includes a number of links (it being noted that in FIG. 8 only the links221 a, 222 a, 223 a for chain 22 a are specifically identified). Eachlink 221, 222, 223 is pivotally coupled with the next link 221, 222, 223in the articulated chain 22 so as to permit rotation about a respectiveaxis (the axes being indicated generally as 225). As is apparent fromFIG. 8, the links 221, 222, 223 are configured such that the link axes225 for all the links 221, 222 within an articulated chain 22 areparallel. Furthermore, each articulated chain 22 a, 22 b, 22 c ispivotally coupled to the rest of the cleaning assembly 19 therebyallowing each of the articulating chains 22 a, 22 b, 22 c to rotateabout an axis that is radially offset from and circumferentiallydirected with respect to the cleaning assembly axis 31 and that isparallel to the axes of rotation 225 of its links 221, 222, 223. In theparticular arrangement of FIG. 8, all of the articulated chains 22 a, 22b, 22 c are pivotally coupled to the remainder of the cleaning assembly19 so as to permit rotation about a common axis 32, which may provide acompact structure.

It should be appreciated that the inclusion of articulated chains issimply one way of configuring the ground-contacting portion such that itprovides a greater friction between itself and the ground when the robot1 carries out turning movements, as compared with when the robot 1carries out straight-line movements. In other examples, theground-contacting portion might, for instance, include a wheel or otherrolling element. Such a rolling element might, for example, be rotatablymounted about an axis that is radially offset from and circumferentiallydirected with respect to the cleaning assembly axis.

FIG. 8 also indicates further details of the cleaning portion 10 of thecleaning assembly 19. Specifically, in the example shown in the drawing,the cleaning portion 10 is made up of a number of elongate scrapingelements 24, each of which is in the form of a blade having two opposingedges used to scrape detritus off the housing 9. As illustrated in FIG.8, the elongate scraping elements 24 are circumferentially arrayed aboutthe cleaning assembly axis 31.

Referring now to FIG. 9, there it is clearly shown that theground-facing side of the housing 2 is generally concave, so as todefine an at least partially-enclosed space 20 between the ground andthe robot during mowing. As may be seen from FIGS. 6 and 7, the cleaningportion 10 of the cleaning assembly 19 and the grass cutting blade 12are disposed within this space 2. As is apparent, the cleaning portion10 removes detritus from the surface of the ground-facing side of thehousing.

As may also be seen from FIG. 9, in the particular example shown theportion of the housing that defines this space 2 is generally bowlshaped. It is also apparent from FIG. 9 that the cleaning assembly 19 isalso generally bowl shaped.

In the particular example shown in FIGS. 6 to 9, the mowing deck 9provides the majority of the ground-facing side of the housing 2, withthe partially-enclosed space 20 being defined by a hollow within themowing deck 9. As is apparent from FIG. 7, the shape of the cleaningportion 10 is complementary to that of the hollow within the mowing deck9.

Reference is now directed to FIGS. 10a and 10b , which show the cleaningassembly 19 in respective positions with respect to the housing 2(specifically, with respect to the mowing deck 9) and thereforeillustrate the movement of the cleaning assembly 19 with respect to thehousing 2. As may be appreciated, the grass cutting blade and thecleaning assembly are rotatable independently of one another. Thehousing 2 and the cleaning assembly 19 are configured such that movementof the passive cleaning assembly with respect to the housing is limitedto a specific range (indicated by arrow C in FIGS. 10a and 10b ).

In more detail, in the particular example shown in FIGS. 6 to 9, and 10a and 10 b, this is accomplished by the provision of co-operatinglimiting features 14 and 15 on each of the cleaning assembly 19 and thehousing 2, specifically, on the mowing deck 9. The co-operating limitingfeatures 14 and 15 are shown clearly in FIGS. 8 and 9. As is apparent,the co-operating limiting features 14 and 15 restrict rotation of thecleaning assembly 19 to a particular angular range C with respect to themowing deck 9 (and therefore the housing 2 more generally). This motionover a limited range is considered to be particularly effective atcleaning the housing of debris. Where the movement of the cleaningassembly with respect to the housing is limited to an angular range, themotion of the cleaning assembly may, for example, be described as beingsubstantially oscillatory or reciprocating.

In the particular example shown in FIGS. 6 to 9, such limitation of themovement of the cleaning assembly with respect to the housing results inthe ground contacting portion staying generally in the same location,namely, towards the rear of the lawnmower.

As illustrated in FIGS. 10a and 10b , the limiting element may beadapted to limit the rotation of the cleaning assembly to a particularangular range. In some cases, suitable angular ranges may be less than90 degrees, less than 60 degrees, or less than 45 degrees.

In the particular example shown, the limiting features are a protrusion15 on the surface of the cleaning portion 10 and a limiter groove 14 onthe mowing deck 9. The protrusion 15 slides within the groove 14, withthe ends of the groove defining the limits of the angular range withinwhich the cleaning assembly 19 may move with respect to the mowing deck9. The angular range within which the cleaning assembly 19 is permittedto move might, for example, be less than 90 degrees, less than 60degrees, or less than 45 degrees.

It will of course be understood that the limiting groove could insteadbe provided on the cleaning portion 10 (or on the cleaning assembly 19more generally) and the protrusion provided on the mowing deck 9 (or thehousing 2 more generally). Moreover, it will be understood that avariety of other limiting features might be used instead.

More generally, while in the example shown in FIGS. 6 to 9, and 10 a and10 b the cleaning assembly includes a ground-contacting portion, this isnot essential. Thus, in other examples, movement of the lawnmower withrespect to the ground may cause the cleaning portion of the passivecleaning assembly to move with respect to the housing (and therebyremove detritus from the housing) as a result, for instance, of themomentum of the cleaning assembly. In such examples, the cleaningassembly might include suitable counterweights.

Further, while in the example shown in FIGS. 6 to 9, and 10 a and 10 bthe cleaning assembly is rotatably mounted on the housing, this is notessential. Thus, in other examples, the cleaning assembly might, forexample, be slidably mounted on the housing. Moreover, it should beunderstood that it is not essential for the cleaning assembly to berotatably mounted on the housing in order that turning movements of thelawnmower cause the cleaning portion to move with respect to thehousing: this could instead be accomplished using such slidably mountedcleaning assemblies.

Furthermore, while in the example shown in FIGS. 6 to 9, and 10 a and 10b the cleaning portion 10 of the passive cleaning assembly 19 does notmove with respect to the housing 2 when the lawnmower 1 moves along astraight line (forwards or backwards) this is of course not essential.For instance, the cleaning assembly might be configured such thatsubstantially all movements of the lawnmower with respect to the groundcause the cleaning portion to move with respect to the housing andthereby remove detritus from the housing. Alternatively, the cleaningassembly might be configured such that only straight-line movements ofthe lawnmower (and not turning movements) with respect to the groundcause the cleaning portion to move with respect to the housing andthereby remove detritus from the housing.

While the foregoing section of the disclosure has made reference to arobotic lawnmower, it is considered that the same principles may beapplied to conventional lawnmowers.

Scraping Cleaning Assembly

While in the previous section and in the example shown in FIGS. 6 to 9,and 10 a and 10 b the cleaning assembly is described and shown as beinga passive cleaning assembly, with movement of the lawnmower with respectto the ground causing a cleaning portion of the passive cleaningassembly to move with respect to the housing and thereby remove detritusfrom the housing, the inventors consider that it may be beneficial toprovide a robotic lawnmower with a cleaning assembly where a scrapingedge of a cleaning portion of the cleaning assembly is moved withrespect to the housing, thereby scraping detritus off thehousing—regardless of whether the cleaning assembly is passive or active(i.e. electrically powered).

Thus, the inventors envisage providing a robotic lawnmower including ahousing and a cleaning assembly for removing detritus from the housing,with the cleaning assembly being moveably mounted on said housing, andwith the robot being configured such that, during use, the cleaningassembly is moved with respect to the housing thereby causing a scrapingedge of a cleaning portion of the cleaning assembly to move with respectto the housing and thereby scrape detritus off the housing. In someembodiments the housing may be generally or substantially bowl shaped.In some embodiments it also envisaged that the cleaning assembly may begenerally or substantially bowl shaped.

An example of a robotic lawnmower according to this concept is therobotic lawnmower 1 shown in FIGS. 6 to 9, and 10 a and 10 b. Asdiscussed in the previous section, during use of this robotic lawnmower,the cleaning assembly 19 is moved with respect to the housing 2 as aresult of the ground-contacting portion 11 contacting the ground duringuse. This in turn causes a number of scraping edges of the cleaningportion 10 of the cleaning assembly 19 to move with respect to thehousing 2 and thereby scrape detritus off the housing 2.

However, a further example according to this concept might, for example,omit the ground contacting portion 11 of the robotic lawnmower shown inFIGS. 6 to 9, and 10 a and 10 b, with movement of the cleaning assemblybeing actively driven by a motor provided within the housing 2. (Ofcourse, the ground contacting portion 11 could also be retained, withsuch a motor being included in addition.)

The principles of operation of the cleaning portion 10 of the cleaningassembly 19 described with reference to FIGS. 6 to 9, and 10 a and 10 bmay equally apply to this concept. Thus, for example, each scrapingedges may have a shape that is complementary to the shape of the portionof the housing from which they remove detritus.

As mentioned above, in the particular example of FIGS. 6 to 9, and inparticular FIG. 8, the cleaning assembly is generally or substantiallyconcave so as to define a second at least partially enclosed space. Thegrass cutting blade is disposed within the second partially enclosedspace. That is to say, in some embodiments the grass cutting blade isgenerally or substantially enclosed by the generally bowl shapedcleaning assembly. As an example, FIG. 8 shows that the scrapingelements 24 are elongate and extend along arc-shaped paths to form thegenerally bowl shaped enclosure. As shown in FIGS. 6-9, and inparticular shown in FIG. 8, elongate scraping elements may becircumferentially arrayed, and may enclose a space between the cleaningassembly and the ground during mowing. The grass cutting blade may bedisposed within this space.

Having a cleaning assembly that encloses the grass cutting blade mayhave the effect that all of the cuttings, and any additional matterthrown up by the blade will be thrown into the space enclosed by thecleaning assembly. This may help ensure that the lawnmower, andespecially the space enclosed by the cleaning assembly is thoroughlycleared of debris. The bowl shape of the cleaning assembly, and of thehousing may also ensure that there are fewer corners or nooks in whichany debris may fall so that it becomes stuck. Nonetheless, the conceptof providing a robotic lawnmower with a cleaning assembly where ascraping edge of a cleaning portion of the cleaning assembly is movedwith respect to the housing, thereby scraping detritus off the housing,is by no means limited to the scraping edges being provided by acleaning portion 10 according to the specific design shown in FIGS. 6 to9, and 10 a and 10 b: a wide variety of alternative constructionsproviding scraping edges may be employed.

While the foregoing section of the disclosure has made reference to arobotic lawnmower, it is considered that the same principles may beapplied to conventional lawnmowers.

Sliding Member

Referring once more to FIG. 6, it is apparent that the robotic lawnmower1 includes a sliding member 8 in addition to two driven wheels 5 a, 5 bfor moving the lawnmower 1 over the lawn.

This sliding member 8 has a ground-engaging surface 13 that ispositioned so as to face towards and to slide over the ground duringsuch movement of the lawnmower 1 over the lawn. The ground-engagingsurface 13 may, as shown in FIG. 6, extend generally parallel to thesurface of the ground.

As is also apparent from FIG. 6, the sliding member 8 and the two drivenwheels are positioned at opposing ends of the lawnmower. The slidingmember 8 and the two driven wheels 5 a, 5 b support respective portionsof the robot's weight.

The inventors envisage that such an arrangement may be employedregardless of whether the other features of the robotic lawnmowerdescribed above with reference to FIGS. 2 to 8 are included, such as thecleaning assembly.

Accordingly, the inventors envisage providing a robotic lawnmowercomprising: two driven wheels for moving the lawnmower over the lawn;and a sliding member having a ground-engaging surface that is positionedso as to face towards and to slide over the ground during such movementof the lawnmower over the lawn; wherein the sliding member and the twodriven wheels are positioned at opposing ends of the lawnmower such thatthe sliding member and the two driven wheels support respective portionsof the robot's weight.

Such a robotic lawnmower may be simple and inexpensive to manufactureand may allow for the robot to be made in a compact design. In contrast,robotic lawnmowers with castor wheels (in addition to drive wheels), maybe relatively more expensive to manufacture and/or may result in largerrobot constructions. Moreover, in comparative testing carried out by theApplicant the castors wheels of such robots are typically much moreprone to falling into holes or hollows in the ground, thus impactingupon the reliability and/or efficiency of such robots.

Returning to FIG. 6, it can be seen that the particular sliding member 8shown therein is adapted to contact the ground over a larger area thaneach of the wheels 5 a and 5 b. A robot with such a sliding member 8 maybe particularly stable, while retaining maneuverability. This relativelylarge contact area of the sliding member may also reduce the risk of thesliding member 8 becoming stuck in holes or hollows in the ground, ascompared with, for example, a castor wheel.

In some embodiments, the sliding member may contact the ground over anarea of at least 40 cm² and preferably at least 50 cm²]. A slidingmember with such an area may also apply less pressure to the ground, andparticularly to the grass after it has been cut, thus keep the grass inbetter condition. It may also sit on the grass which, after being cut,should be at substantial the same height, and therefore ensure thestability of the lawnmower further. Sliding members of alternativeembodiments may also have a similar area.

As may also be seen from FIG. 6, the sliding member 8 is located at therear of the lawnmower 1 with respect to its forwards direction ofmovement (F). However, this is not essential for the implementation ofthe general concept identified above; thus, in other cases the slidingmember 8 might, for example, be located at the front of the lawnmower 1.Indeed, in some constructions, the robot may be more maneuverable whenmoving in the direction of the end at which the sliding member 8 islocated.

Accordingly, for some applications it might be appropriate to definethis direction within the robot's programming as being the forwardsdirection. In addition, the robot may be more effective at cuttinglonger grass when moving in the direction of the end at which thesliding member 8 is located.

As may be seen in FIGS. 6 and 11, the portions of the sliding member 8adjoining the ground-engaging surface 13 are rounded. This may aid thesmooth sliding of the ground-engaging surface 13 over the ground.

The sliding member 8 may be mounted on the housing 2 of the robot 1 suchthat there is no significant change in the orientation of the slidingmember 8 (and therefore the ground-engaging surface 13 also) withrespect to the housing 2 as the ground-engaging surface 13 slides overthe ground. However, as will be discussed in further detail below, themounting of the sliding member 8 on the housing 2 may allow for somemovement of the sliding member relative to the housing.

FIG. 11, which is a plan view of the underside of the robot of FIGS. 2to 6, illustrates clearly the relative disposition of the sliding member8 and the wheels 5 a, 5 b. As may be seen, the wheels 5 a, 5 b arespaced apart along a wheel axis 33 and the sliding member 8 (andtherefore the ground-engaging surface 13 also) is located mid-waybetween the wheels 5 a, 5 b with respect to the wheel axis 33 whilebeing offset from it.

As may also be seen from FIG. 11, the sliding member 8 is shaped suchthat the ground-engaging surface 13 is elongate in a direction parallelto the wheel axis 33. This may provide lateral stability to the robot 1.

As stated above, the sliding member 8 and the two driven wheels 5 a, 5 bsupport respective portions of the robot's weight (and indeed, in somecases, they may together support substantially all of the robot'sweight). Hence, or otherwise, the centre of mass of the lawnmower maylie between the two driven wheels and the sliding member.

Suitable balancing of the amounts of these portions of the robot'sweight may improve the performance of the robot. For instance, becausethe sliding of the ground-contacting surface 13 over the lawn maycontribute significantly to the friction experienced by the robot whilemoving (given that the sliding member 8 is neither actively driven orable to roll on the surface of the lawn) it may be appropriate for therobot's weight to be balanced such that the portion of the weightsupported by the sliding member 8 is less than the portion of the weightsupported by the two driven wheels 5 a, 5 b.

Testing carried out by the Applicant suggests that, because the grass ofa lawn is relatively “soft”, the friction provided by the sliding member8 may be roughly proportional to the pressure exerted by the slidingmember (through the ground-contacting surface 13) on the grass. Testscarried out by the Applicant suggest that efficient movement may beexperienced where the pressure is less than 35 g/cm² and, in some cases,less than 25 g/cm². In addition, or instead, a lower pressure may resultin the lawn being less squashed/compressed by the sliding member than analternative ground contacting portion such as a caster or driven wheel.

In other cases, the friction provided by the sliding member 8 may beroughly proportional to the weight supported by the sliding member 8.Tests carried out by the Applicant suggest that efficient movement maybe experienced where the weight supported by the sliding member is lessthan 3 kg, in some cases less than 2.5 kg and, in particular, less than2 kg.

Conversely, for stable movement over the lawn (avoiding, for instance,the robot bouncing up and down on its sliding member 8 when travellingover bumps or hollows in the lawn), the sliding member 8 should supportat least some of the weight of the robot. Tests with prototypes suggestthat where the sliding member 8 supports at least 15% of the weight ofthe robot, stable movement may be experienced (though this is by nomeans essential and certain robots where the sliding member 8 supportsless than 15% of the robot's weight may experience reasonably stablemovement). Improvements in stability were seen where the sliding member8 supports at least 20% of the weight of the robot.

As briefly mentioned above with reference to FIG. 1, the power system200 of the robot of FIGS. 2 to 6 may include a rechargeable powersource. While in the description above with reference to FIG. 1 and toFIGS. 4 and 5 it was proposed that the power system 200 would includecharging contacts (e.g. provided within holes at either end of slot 7)for connection to an external power source (e.g. provided at a dockingstation), it is envisaged that the power system may instead (or perhapsin addition) include a wireless power receiver: a receiver that does notrequire a direct electrical connection to a power supply in order toreceive electrical power. The wireless power receiver may be configuredto wirelessly receive electrical power from a wireless power transmitterexternal to the robot (for example located in a docking station) and tothereby charge the rechargeable power source.

In addition, it is considered that such a wireless power receiver mayconveniently be located (at least partially) within the sliding member8. This arrangement may allow the robot to charge its internal powersource at a suitably configured docking station by simply resting theground engaging surface 13 of the sliding member 8 on top of a surfaceof the charging station that includes a wireless power transmitter.

The efficiency of wireless power transmission is in general limited bythe cross-sectional area presented by the wireless power receiver to thewireless power transmitter and/or the proximity of the wireless powerreceiver to the wireless power transmitter. By locating the wirelesspower receiver within the sliding member 8, one or both of theselimiting factors may be addressed: as the wireless transmitter will bein proximity to the generally large area of the (externally facing)ground-contacting surface 13, it may therefore present a largecross-sectional area to the exterior of the robot and thereforepotentially to the wireless power transmitter; in addition, theproximity of the wireless transmitter to the ground-contacting surface13 implies that the wireless transmitter will be in proximity to theexterior of the robot and therefore potentially the wirelesstransmitter. For the same reasons, it may be particularly beneficial tolocate the wireless power receiver adjacent to the ground-engagingsurface 13.

The wireless power receiver may be configured for any appropriatewireless power transfer technology, such as inductive coupling, resonantinductive coupling, capacitive coupling and the like. In many cases, thewireless power receiver may include a coil, for example an inductioncoil. In order to provide a large cross-section for receiving thewireless power signal transmitted by the wireless power transmitter,this coil may be arranged such that its axis is normal to theground-engaging surface 13.

Of course, it should be understood that the inclusion of such a wirelesspower receiver is purely optional and that charging contacts couldinstead be utilised.

Arrangement of Ground Contacting Members and Blade

As discussed above, the robot shown in FIGS. 2 to 6 includes a pair ofdrive wheels 5 a, 5 b spaced apart along a wheel axis 33 and a slidingmember 8. As also discussed above, the drive wheels 5 a, 5 b and thesliding member 8 all contact the ground so as to support the housing 2above the ground. The wheels 5 a, 5 b are driven so as to rotate aboutthe wheel axis 33, thereby propelling the lawnmower 1 over the ground.

FIG. 11, which is a plan view of the underside of the robot of FIGS. 2to 6, illustrates the arrangement of the robot's cutting blade 12 withrespect to the driven wheels 5 a, 5 b and the sliding member 8. As thedrawing shows, the grass cutting blade 12 is driven by the lawnmower soas to move with respect to the housing, thereby sweeping out acorresponding cutting area (indicated by dashed circle 51) beneath thehousing 2.

The drawing also indicates in dashed line the polygonal footprint 50defined by the ground-contacting members of the robot, which are thoseelements that support the housing 2 above the ground: in the particularexample shown, driven wheels 5 a, 5 b and sliding member 8. Moreparticularly, if each of the ground-contacting members is regarded ascontacting the ground over a respective ground contact region, theground contact footprint 50 may then considered as being defined by thepolygon bounding all of these ground contact regions. As will beapparent, the polygon defining the ground contact footprint 50 takes astraight-line path between the ground contacting regions.

As FIG. 11 shows, a part 51 a of the cutting area 61 for the cuttingblade 12 lies beyond the perimeter of the ground contact footprint 50.Conversely, the remaining part 51 b of the cutting area 51 for thecutting blade 12 lies within the perimeter of the ground contactfootprint 50.

Such an arrangement of the cutting area of the blades with respect tothe ground contact footprint 50 may enable the robot to mow all the wayto the edge of the lawn with little risk that the robot will fall offthe edge of the lawn, since the ground contacting members may remain asafe distance from the edge of the lawn (or at least on the lawn) whilethe cutting blade cuts an area that extends up to or beyond the edge ofthe lawn.

In the particular arrangement illustrated in FIG. 11, the part 51 a ofthe cutting area 51 that lies beyond the perimeter of the ground contactfootprint 50 is at the front of the lawnmower with respect to itsforwards direction of movement (indicated by F in the drawing). This mayenable the robot to safely cut to the edge of the lawn where itapproaches in the forwards direction.

Furthermore, FIG. 11 illustrates that the driven ground contactingmembers (which in the particular example shown in FIGS. 2, 3, 4, 5, 6and 11 are wheels) may be in front of the non-driven ground contactingmembers (which in the particular example shown in FIGS. 2, 3, 4, 5, 6and 11 is a sliding member) relative to the direction of forwardsmovement, F. Having the driven ground contacting members positionedforwards of the non-ground contacting members in the direction offorward motion may reduce the risk of the driven ground contactingmembers moving outside of the boundary of the lawn when mowing right upto the boundary.

Moreover, as illustrated in FIG. 12, the robot 1 (e.g. the controlsystem 100 thereof) may be specifically programmed such that, when itsnavigation system 300 indicates that it is in the vicinity of theboundary 40 of its working area (e.g. part of, or the whole of the lawn)and it is approaching the boundary 40, it arrives at the boundary at apredetermined angle with respect to the nearest part of the boundary,for instance by carrying out a turning movement. In the particularexample shown in FIG. 12, this predetermined angle is 90 degrees.However, in other arrangements (for example as a result of differentblade arrangements), a different predetermined angle might be definedwithin the robot's programming. In many cases, however, thepredetermined angle will be at least 45 degrees and, often, at least 60degrees, so that the robot arrives at the boundary moving generallyforwards, as opposed to moving parallel to the boundary.

Hence, or otherwise, the robot may be programmed such that, upon thenavigation system indicating that the robot is in the vicinity of theboundary and is approaching the boundary, it moves along a path that iscalculated such that the parts of the cutting areas beyond the groundcontact footprint are applied all the way to (and in some cases over)the boundary, but without the ground-contacting members crossing theboundary.

Having moved along a path, such as that shown in FIG. 12, that takes therobot up to the boundary of the area, the robot may then reverse awayfrom the boundary (for example by driving the wheels in the oppositerotational sense). Such a movement pattern may be contrasted with thosewhere the robot is moving parallel to the boundary at its point ofclosest approach.

The navigation system may suitably include a number of boundary distancesensors for estimating the robot's current distance from the boundary.As discussed above in the “Overview” section, examples of such sensorsinclude: coils for sensing a magnetic field that is induced by a wireloop, which delimits the area and transmits an alternating current;range finders, such as ultrasonic or laser range finders, which canmeasure a distance from a hard delimiter such as a fence or wall; 2D or3D machine vision systems that can evaluate a distance to marked ornatural delimiters (for example, a grass-classifying algorithm may beused to determine the edge of the lawn).

Of course, the navigation system could in addition or instead rely onsensors operable to sense the relative motion of the robot and/orsensors operable to determine the robot's absolute position within thearea. In such cases, information defining the boundary (e.g.co-ordinates) may be stored by the robot. The control system 100 maythen reference this information so as to determine how far its currentposition (as determined by the navigation system 300) is from theboundary.

The approach illustrated in FIG. 12 may be contrasted with thatdescribed in EP2806325A, where the robot may carry out a gradual turnwhere, at the closest approach distance to the boundary, it is movingtangentially of the boundary. Nonetheless, a number of the techniquesdisclosed in EP2806325A might be applied to a movement pattern as shownin FIG. 12, where the robot 1 arrives at the boundary movingperpendicular to the boundary 40.

The robot shown in FIGS. 2-11 is particularly suited to movement in bothforwards and rearwards directions. This is because, as viewed fromvertically above the lawnmower 1, the ground contacting portion of themowing deck 9 is located on one side of the wheel axis 33 and theground-engaging surface 13 of the sliding member 8 is located on theopposite side of the wheel axis. In the particular example shown, thesefeatures are indeed located at opposite ends of the lawnmower 1 (again,when viewed from vertically above the lawnmower 1), specifically, at theforwards and rearwards ends. With such an arrangement, the slidingmember 8 may enable the moveably suspended mowing deck 9 to set themowing height particularly effectively, enabling the lawnmower 1 to dealwith tall grass when moving either forwards or backwards.

A further feature of the robot of FIGS. 2-11 that assists with movingforwards and rearwards, is that the grass cutting blade is arranged suchthat the axis of rotation of each grass cutting blade substantiallyintersects with the wheel axis 33. This may, for example, allow thedrive motor for the grass cutting blade to be supported above the wheelaxis 33, balancing the weight of the robot whether moving forwards orbackwards. Of course, the same feature may be implemented regardless ofwhether the robot is programmed to regularly move both forwards andbackwards.

While in the arrangement shown in FIG. 10 only one grass cutting bladeis employed, it should be understood that multiple grass cutting bladesmight be provided, with each sweeping out a respective cutting areabeneath the housing. In such a case, the cutting blades may be arrangedso that at least part of one or more of these cutting areas (and in somecases each of these cutting areas) is beyond the perimeter of the groundcontact footprint.

More generally, while the robot shown in FIGS. 2-6 and 11 is propelledover the ground by drive wheels 5 a, 5 b it is considered thatcontinuous tracks or some other type of drive ground-contacting membersmight be used instead. Thus the drive wheels described above should beunderstood as an example of ground-contacting members that are driven soas to move relative to the housing and to the ground thereby propellingthe lawnmower over the ground.

In addition, while the robot shown in FIGS. 2-6 and 11 includes thesliding member 8, it is considered that any suitable type ofground-contacting member could be substituted, whether passive, such asa castor wheel, or other freely rolling member, or actively driven, suchas further driven wheels, continuous tracks and the like.

The applicant therefore views the robot of FIGS. 2-6 and 11 as being aspecific example of the much more general concept, whereby there isprovided a robotic lawnmower comprising: a housing; a plurality ofground-contacting members, which during use each contact the ground overa ground contact region, the ground-contacting members therebysupporting the housing above the ground, at least some of saidground-contacting members being driven so as to move relative to thehousing and to the ground thereby propelling the lawnmower over theground, a ground contact footprint being defined by the polygon boundingall of said ground contact regions; and at least one grass cuttingblade, each of which is driven by the lawnmower so as to move withrespect to the housing, thereby sweeping out a respective cutting areabeneath the housing; wherein at least part of one or more of the cuttingareas is beyond the perimeter of said ground contact footprint.

Combinations

It is envisaged that the concepts discussed above may be combined in avariety of ways within a robotic lawnmower.

For example, concepts disclosed in the “Arrangement of the groundcontacting members and blade” section may be implemented in a roboticlawnmower in combination with the concepts disclosed in the “SlidingMember” section. Furthermore, any or all of the concepts disclosed inthe “Sliding Member” and “Arrangement of the ground contacting membersand blade” sections may be implemented in a robotic lawnmower incombination with either of the concepts disclosed in the “PassiveCleaning Assembly” and “Scraping Cleaning Assembly”.

Of course, it will be appreciated that these are only examples; stillfurther combinations are envisaged.

More generally, it should be appreciated that other examples andvariations are contemplated within the scope of the appended claims.

It should be noted that the foregoing description is intended to providea number of non-limiting examples that assist the skilled reader'sunderstanding of the present invention and that demonstrate how thepresent invention may be implemented.

1. A lawnmower comprising: a housing; and a passive cleaning assemblyfor removing detritus from the housing, the passive cleaning assemblybeing moveably mounted on said housing; wherein movement of the lawnmower with respect to the ground causes a cleaning portion of thepassive cleaning assembly to move with respect to the housing andthereby remove detritus from the housing.
 2. The lawnmower of claim 1,wherein the passive cleaning assembly further comprises aground-contacting portion, which contacts the ground during use, therebycausing said cleaning portion to move with respect to the housing duringmovement of the lawnmower.
 3. The lawnmower of claim 1, wherein turningmovements of the lawnmower cause the cleaning portion to move withrespect to the housing and thereby remove detritus from the housing. 4.The lawnmower of claim 1, wherein the passive cleaning assembly isrotatably mounted on the housing, such rotation being about a cleaningassembly axis.
 5. The lawnmower of claim 4, wherein the cleaningassembly axis is substantially normal to the ground.
 6. The lawnmower ofclaim 1, further comprising a grass cutting blade, which is driven bythe lawnmower so as to rotate with respect to the housing about a bladeaxis, wherein the passive cleaning assembly is rotatably mounted on thehousing about a cleaning assembly axis, and wherein the blade axis issubstantially aligned with the cleaning assembly axis.
 7. (canceled) 8.The lawnmower of claim 6, wherein the housing has a ground facing side,which is generally concave, so as to define an at leastpartially-enclosed space between the ground and the lawnmower duringmowing, the cleaning portion and the blade being disposed within saidspace, wherein the cleaning portion removes detritus from at least aportion of the surface of said ground-facing side.
 9. (canceled)
 10. Thelawnmower of claim 2, wherein the ground-contacting portion isconfigured such that an amount of friction between the ground-contactingportion and the ground is substantially greater when the lawnmowercarries out turning movements, as compared with when the lawnmowercarries out straight-line movements.
 11. The lawn mower of claim 2,wherein the ground-contacting portion is adapted to contact the groundat the rear of the lawnmower with respect to its forward direction ofmovement.
 12. The lawnmower of claim 2, wherein the ground-contactingportion comprises at least one articulated chain, which contact theground during movement of the lawnmower.
 13. The lawnmower of claim 12,wherein each chain comprises a plurality of links, each link beingpivotally coupled to the next in the chain so as to permit rotationabout a respective axis, the link axes for all of the links within achain being parallel.
 14. The lawnmower of claim 13, wherein the passivecleaning assembly is rotatably mounted on the housing, such rotationbeing about a cleaning assembly axis, and wherein each articulated chainis pivotally coupled to the remainder of the cleaning assembly, so as topermit rotation about an axis that is radially offset from andcircumferentially directed with respect to said cleaning assembly axisand that is parallel to the axes of rotation of its links.
 15. Thelawnmower of claim 14, wherein there are provided a plurality of saidarticulated chains and wherein all of the articulated chains arepivotally coupled to the remainder of the cleaning assembly, so as topermit rotation about a common axis.
 16. The lawnmower of claim 1,further comprising a limiting element configured to limit the movementof the passive cleaning assembly with respect to the housing to adefined range.
 17. The lawnmower of claim 16, wherein the passivecleaning assembly is rotatably mounted on the housing, such rotationbeing about a cleaning assembly axis, and wherein the limiting elementis adapted to limit the rotation of the passive cleaning assembly withrespect to the housing about the cleaning assembly axis to a particularangular range, which is preferably less than 90 degrees, more preferablyless than 60 degrees, still more preferably less than 45 degrees. 18.The lawnmower of claim 1, wherein the cleaning portion comprises aplurality of elongate scraping elements.
 19. The lawnmower of claim 18,wherein each scraping element is shaped as a blade having two opposingedges, which are each configured to scrape detritus off the housing. 20.The lawnmower of claim 18, wherein the passive cleaning assembly isrotatably mounted on the housing, such rotation being about a cleaningassembly axis, and wherein the plurality of elongate scraping elementsare circumferentially arrayed about the cleaning assembly axis.
 21. Thelawnmower of claim 1, wherein the lawnmower is a robotic lawnmower. 22.A lawnmower comprising: a housing; and a cleaning assembly for removingdetritus from the housing, the cleaning assembly being moveably mountedon said housing; the lawnmower being configured such that, during use,the cleaning assembly is moved with respect to the housing therebycausing a scraping edge of a cleaning portion of the cleaning assemblyto move with respect to the housing and thereby scrape detritus off thehousing.
 23. The lawnmower of claim 22, wherein the cleaning assembly isrotatably mounted on the housing, such rotation being about a cleaningassembly axis, and wherein the cleaning assembly axis is substantiallynormal to the ground.
 24. (canceled)
 25. The lawn mower of claim 23,further comprising a grass cutting blade, which is driven by thelawnmower so as to rotate with respect to the housing about a bladeaxis, and wherein the blade axis is substantially aligned with thecleaning assembly axis.
 26. The lawn mower of claim 25, wherein thegrass cutting blade and the cleaning assembly are rotatableindependently of one another.
 27. (canceled)
 28. The lawnmower of claim25, wherein the housing has a ground facing side, which is generallyconcave and generally bowl shaped, so as to define an at leastpartially-enclosed space between the ground and the lawnmower duringmowing, the cleaning portion and the blade being disposed within saidspace.
 29. (canceled)
 30. The lawnmower of claim 28, wherein thecleaning assembly is substantially concave and generally bowl shaped soas to define a second at least partially enclosed space, the grasscutting blade being disposed within the second partially enclosed space.31. (canceled)
 32. The lawnmower of claim 28, wherein the scraping edgeof the cleaning portion scrapes detritus off at least a portion of thesurface of said ground-facing side.
 33. (canceled)
 34. The lawnmower ofclaim 23, further comprising a limiting element, wherein the limitingelement is adapted to limit the rotation of the cleaning assembly withrespect to the housing about the cleaning assembly axis to a particularangular range, which is preferably less than 90 degrees, more preferablyless than 60 degrees, still more preferably less than 45 degrees. 35.The lawnmower of claim 22, wherein the cleaning portion comprises aplurality of elongate scraping elements.
 36. The lawnmower of claim 35,wherein each scraping element is shaped as a blade having two opposingedges, which are each configured to scrape detritus off the housing. 37.The lawnmower of claim 35, wherein the cleaning assembly is rotatablymounted on the housing, such rotation being about a cleaning assemblyaxis, and wherein the plurality of elongate scraping elements arecircumferentially arrayed about the cleaning assembly axis.
 38. Thelawnmower of claim 22, further comprising at least one motor configuredto move the cleaning assembly with respect to the housing.
 39. Thelawnmower of claim 22, wherein the lawnmower is a robotic lawnmower.40.-73. (canceled)